Originally Posted by Mike Benvo
Flashing it back to stock before taking it to the dealer is a waste of time (unless you're dealing with a catastrophic issue and they had clear indications that there may have been 'tampering'.
A proper tune will not cause fault codes or show any indication that the file is modified.
Putting it back to stock does not modify the freezeframe data, it is stored in a section of the left processor that can not be modified without opening up the DME. The only reason you might want to flash to stock (or flash to a different revision of the tune) is to turn the secondary air pump back on. But most dealers wouldn't notice that the car wasn't louder on startup.
But what if you're catless? No check engine light? Wouldn't you then perhaps want to flash back to stock as to not raise suspicions?